www/node8: Update 8.15.0 -> 8.15.1

This is a security release. All Node.js users should consult the security
release summary at
https://nodejs.org/en/blog/vulnerability/february-2019-security-releases/
for details on patched vulnerabilities.

MFH: 2019Q1
Security: b71d7193-3c54-11e9-a3f9-00155d006b02
Sponsored by: Miles AS